1) Field of the Invention
This invention relates to a hand assisted lamination (HAL) system process and apparatus for forming and compacting composite material in order to make laminated articles that may have three-dimensional (3-D) contoured surfaces. Three-dimensional contoured surfaces are surfaces having an x dimension , a y dimension, and a z dimension (the z dimension being the vertical dimension). More particularly, this invention relates to such a process and apparatus in which plies of a fiber-reinforced prepreg composite material are laid one at a time and then formed and compacted against a lay-up tool that has a three-dimensional contoured surface. This invention can also be described as a computer aided composite material lamination system. The HAL system will have a favorable environmental impact because its use will eliminate a significant amount of waste consisting of prepreg material which was generated unintentionally as the result of operator error in the prior hand lay-up lamination process.
2) Description of the Background Art
In the manufacture of commercial aircraft, the use of fiber-reinforced composite materials to fabricate laminated structural components, for both the primary and the secondary structures of aircraft, is becoming increasingly widespread because of the resulting weight savings which produce fuel savings which are cost savings for commercial airline operators. The fabrication process for producing advanced composite laminates requires that the plies of the prepreg composite material, such as graphite fiber-epoxy materials, be laid one at a time and that the plies be accurately located in various orientations on a lay-up tool (also known as a lay-up mandrel). Each ply must be formed and compacted to conform to the contour of the lay-up tool prior to laying down the next ply. The compaction of each ply serves to remove entrapped air between the plies in order to produce a laminated structural component that is free of porosity and voids. Therefore, each ply must be accurately located and oriented on top of the previous ply and the compaction of each ply against the previous ply on the lay-up tool must be performed before the addition of the next ply. In the prior hand lay-up lamination process, these steps were labor intensive and time consuming; therefore, the resulting structural components were costly.
Thus, there has been a long-felt need to mechanize or automate the fabrication of laminated structural components for aircraft and for other end-uses, such as in automobiles, in order to reduce the cost of the components. In Mittelstadt et al. U.S. Pat. No. 4,475,976, there is disclosed an automated process and apparatus for forming certain types of composite material articles, for example, channel stringers for aircraft. In the example of a channel stringer, a ply of fiber-reinforced composite material in the form of a tape was laid by a tape laying head carried by a gantry. The tape ply was laid onto a lay-up mandrel having a generally U-shaped cross section and having a vacuum-ported upper surface. The tape ply was laid onto the top web of the mandrel, with the side edges of the tape ply being laid in a cantilevered fashion. A flexible bag was inflated into a stretched condition and lowered over the top of the mandrel and the tape ply. The bag rolled over the mandrel to form the tape ply down over the mandrel. As the bag rolled over the mandrel, it folded the tape ply along the two contoured bend lines between the web and flanges of the mandrel and simultaneously restrained the tape ply from folding along a straight line. When fully deployed, the bag engaged a seal carried by the mandrel. A vacuum was then applied through the vacuum ports of the mandrel to evacuate the air from the area between the bag and the mandrel within the seal to compact the tape ply. Each ply of the composite tape material was thus formed and compacted before laying another ply of the tape.
The process of Mittelstadt et al. U.S. Pat. No. 4,475,976, works well and is cost effective in the case where a ply of fiber-reinforced composite material in the form of a tape can be laid by a tape laying head carried by a gantry. But in the case of structural components having more complex three-dimensional contours (i.e., where a tape laying head carried by a gantry, such as described in the Mittelstadt et al. patent above, is not feasible for laying down the plies of prepreg material), a costly hand lay-up lamination process using large hand lay-up templates was employed in which a human operator would lay by hand each pre-cut ply of prepreg composite material in its proper location and orientation on the lay-up tool (i.e., on the lay-up tool or on top of the previous ply of prepreg). For each structural component, the hand lay-up lamination process involved the use of one or more of these hand lay-up templates. The hand lay-up templates were made of a flexible material, had various openings cut therein, and had ply numbers and other indicia written on the top surface of the template adjacent to each opening to guide the operator in using the template. The prior hand lay-up lamination process was accomplished as follows.
The correct lay-up template (hereafter referred to as the hand lay-up template) was located by the operator and placed over the lay-up tool. Each pre-cut ply of prepreg composite material, in its proper sequence, required placing the template over the lay-up tool and securing the template in the proper location and orientation using tooling pins. The operator then made marks through the template openings for that ply number, thereby marking the outline of the next ply on the surface of the previous ply. The operator removed the template from the lay-up tool, and then laid down and formed the ply to conform to the contour of the lay-up tool, the ply being in its proper location and orientation, as indicated by the outline markings, on top of the previous ply.
To compact the ply (that is, to remove the entrapped air between the new ply and the previous ply), the operator placed an FEP sheet (a release sheet made of Mylar coated with Teflon) over the lay-up tool and then on top of the FEP the operator placed a layer of breather material (air weave or fiberglass cloth). On top of those two layers, the operator placed a layer of nylon bagging material that was sealed around the periphery of the lay-up tool using a tacky tape material. Vacuum was then drawn through ports in the nylon bag to compact the ply. The time and pressure were controlled and monitored by the operator. The vacuum was released and the bag layers were removed. The entire process was then repeated for each succeeding ply of prepreg composite material until the required number of plies for the laminated structural component was achieved.
The prior hand lay-up process had the following disadvantages or problems: (1) The possibility of human error by retrieving the wrong hand lay-up template and/or marking an out-of-sequence ply. (2) Costs were incurred for creating, storing, and using the templates. (3) Hand labor was required to fully form the plies. This was costly and contributed to operator fatigue and health problems. (4) The breather material and nylon bagging material would be discarded after each part was completely laminated and this represented recurring fabrication expense. (5) In compacting, the placement of the three layers of material and the sealing of the nylon bagging were hand operations which were fatiguing to operators and not readily automated. They represented recurring labor expense. (6) The critical process parameters of vacuum pressure and time were not consistently applied by human operators. (7) The several layers of material (release sheet, breather, and nylon bagging) were not very stretchable, and thus required careful placement and pleating of the layer of nylon bagging into or onto complex three-dimensional part geometries. Failure to do so caused defects in the final part.